The invention concerns elastic film materials and laminates containing elastic film materials.
Thin elastic film materials, nonwovens and other like web materials are used with increasing frequency in the disposable or personal use garment product area, garment meaning a product used on, or in association with, a body (human or animal). Specifically, such uses include disposable diapers, training pants, incontinence articles, sanitary napkins, bandages, surgical drapes and gowns, medical nonwovens, face masks, sport wraps and the like. Generally, these elastomeric materials are formed of conventional elastomers which generally exhibit elastic properties in substantially all directions, particularly if in the form of an elastic film. However, for some specific applications, it is desirable to have materials which are primarily elastic in only a single direction, i.e., anisotropic elastic materials. A large number of patent applications and patents have been directed towards this problem, providing a wide variety of solutions. The most common approach in the art has been to laminate an elastic web material to a second web material that is easily stretched in one direction but not in the transverse direction. PCT application No. WO 96/10481 discusses a version of this approach stating that a common practice has been to produce a so-called "stretch-bonded laminate". With these stretch-bonded laminates, an elastic film or nonwoven, or like elastic web, is elongated in one direction. While elongated, the elastic web is either continuously or point-bonded to an inelastic web material. Afterwards, tension is released and the elastic web is allowed to recover in the direction opposite to its elongation. The attached inelastic web material then puckers making the stretch-bonded laminate readily extensible in the direction of the elastic web's elongation but not in the transverse direction. The laminate can then be restretched up to the point of previous elongation of the elastic web. However, this puckering is indicated as undesirable for some applications. In order to overcome the puckering problem, the WO 96/10481 application proposes using an inelastic nonwoven web material with a large number of substantially parallel slits. This slit nonwoven web material is then attached to an untensioned elastic web material. When the laminate is then stretched in a direction perpendicular to the direction of the slits the laminate stretches and recovers without the formation of puckers or gathers in the inelastic nonwoven web.
Some patent documents which discuss or are directed at the prior art methods disclosed in the above PCT application include European Patent Application No. 693585 A2 and U.S. Pat. Nos. 4,413,623; 4,606,964 and 4,720,515 all of which stretch an elastic web material and then point bond, or otherwise bond the stretched elastic web to a relatively inelastic web material, which inelastic web material subsequently gathers when the tensioned elastic web is allowed to recover. In a variation of this, U.S. Pat. No. 4,525,407 joins elastic and inelastic web materials while the elastic web is untensioned. The laminate is point bonded and then stretched under tension strong enough to cause the inelastic web material to permanently deform, which deformed inelastic material then puckers or gathers upon recovery of the elastic material. A method similar to this is disclosed in, e.g., U.S. Pat. Nos. 5,527,304 and 5,167,897. The materials formed in these patents have been termed "zero strain" elastic materials in that the inelastic and elastic web materials are joined without either being under strain. The one or more inelastic web materials and the elastic web materials are then subject to particular forms of incremental stretching between meshed corrugating rolls. Other randomly gathered materials can also be produced using heat shrinkable elastics such as disclosed in U.S. Pat. Nos. 3,819,404 and 3,912,565.
Also disclosed is a nonwoven inelastic web corrugated between geared teeth or corrugating rolls. While the inelastic web is corrugated, it is bonded to an elastic web material by extrusion lamination or adhesive lamination such as disclosed, respectively, in PCT Application No. WO 95/34264 and Japanese Kokai No. HEI 7-213554. These laminated materials have relatively large, uniform and regular gathers as compared to the other methods described above. These materials also have relative uniform elastomeric properties and are aesthetically pleasing. However, these elastic laminates are generally very thick and as such can be unsuitable for certain types of uses requiring a flatter profile elastic material.
Anisotropic elastic materials having cross-directional elasticity are disclosed, for example, in U.S. Pat. Nos. 5,514,470; 4,965,122; 5,226,992; 4,981,747 and European Patent No. 707106. In these patents, there is used a "neckable" inelastic nonwoven web material. Suitable neckable nonwoven webs include spunbond, meltblown or bonded carded webs. The neckable nonwoven webs are stretched in a machine direction in a manner which causes the inelastic web materials to neck (i.e., decrease in width) in the cross direction. While the nonwoven web materials are necked in this manner they are joined to an elastic web such as a film or nonwoven, either continuously or in a point bonded manner. The resulting laminate material is generally inelastic in the machine direction while being substantially elastic in the cross direction up to the original cross dimensional width of the reversibly necked material.
An inelastic nonwoven web material exhibiting directional elastic-type properties is disclosed in U.S. Pat. No. 3,949,128. In this patent, a continuous filament nonwoven web, as would be produced by a spunbond process, is point bonded and then either stretched in the machine direction or microcreped in the machine direction and then subjected to heat setting. Depending on whether the heat set web material is stretched or microcreped, it exhibits a CD elastic-like property or MD elastic-like property, respectively.
U.S. Pat. No. 5,366,793 discloses an anisotropic elastomeric nonwoven fibrous web of meltblown elastomeric fibers. The anisotropic behavior is obtained by aligning the fibers with an airstream to produce a web with a higher peak load tension in the direction of fiber orientation.
In U.S. Pat. Nos. 5,344,691; 5,501,679 and 5,354,597 there is disclosed multilayered elastomeric films including those having an elastomeric central layer with one or two outer film layers of a relatively inelastic material. The multilayer films are coextruded so as to produce thin inelastic film layers and a relatively thick elastic film layer. These coextruded film materials are termed stretch activated elastic (SAE) and are substantially inelastic as formed but if stretched in one direction and allowed to recover will exhibit uniaxial elastic properties in the direction in which the laminate has been stretched and recovered. The materials which have been stretched uniaxially will exhibit substantially anisotropic elastic behavior. The anisotropic elastic behavior in these coextruded laminates can be accentuated as described in U.S. Pat. No. 5,462,708 by subjecting a uniaxially stretched laminate to a deactivating heat treatment, while in the stretched condition. The heat treatment is such that the elastic recovery force of the elastic material is allowed to dissipate without substantially affecting the orientation of the inelastic skin materials. The heat treated laminate material is then stretched in a second cross direction and allowed to recover as described above. The resulting material is exceedingly strong in the original stretch direction and elastic in the cross direction. Generally, these SAE materials are extremely advantageous where a low profile-type elastic web is required, which elastics can have either isotropic or anisotropic elastic properties as may be required.
An anisotropic, single-layer, film-type elastic is disclosed in Japanese Patent Kokai No. 5-186611, this patent discloses extrusion of a blend of an ABA block copolymer with polystyrene where the polymers are exemplified as blended at a ratio of from 50 to 99 percent block copolymer to 1 to 50 percent polystyrene. The resulting material produced exhibits anisotropic elastic behavior. Polypropylene is exemplified as not working to produce anisotropic behavior. Materials of the type disclosed in this Kokai have been found to have relatively low tear resistance and unless suitably treated with an antiblocking agent or the like tend to exhibit high blocking behavior.
There is a continuous need for further forms of anisotropic elastic webs suitable for use in a wide variety of potential applications which web materials are easy to manufacture, form readily into a roll and subsequently easily unwound without blocking, handled and converted into its final form for use on a limited-use garment and the like.